Cerebral glutamate levels over two years in initially antipsychotic-naïve first-episode patients with psychosis are related to clinical symptoms and cognition

Although emerging evidence supports glutamatergic dysfunction in schizophrenia, clinical trials with glutamatergic compounds have overall been negative. This may be due to changes in glutamate levels during the course of illness.

To address this, we measured glutamate levels in dorsal anterior cingulate cortex (dACC) and left thalamus in 57 initially antipsychotic-naïve patients with first-episode psychosis (FEP) aged 22.6 ± 5.0 years (58% females) and 55 healthy controls (HC) on a 3T MR scanner at baseline, after six weeks (48 FEP and 53 HC), six months (37 FEP and 49 HC), and two years (35 FEP and 45 HC). Positive and negative symptoms and cognitive function in tests of attention and spatial working memory were assessed at all visits. Linear mixed models were used in statistical analyses.

We found lower glutamate levels in dACC in FEP (p=0.03) that was associated with deficits in attention at all visits (p<0.05). Thalamic glutamate levels did not differ between groups, but higher levels were related to more pronounced positive symptoms at all visits (p=0.02). The relation between thalamic glutamate levels and negative symptoms was altered over time (negative symptoms*time: p=0.003) due to a significant positive association after two years (p=0.04) but not at other visits. For other metabolites, thalamic NAA were lower in FEP (p=0.04) and total creatine was increased after 6 weeks treatment (p=0.01), whereas dACC glx levels were lower after two years (p=0.02).

The results suggest that greater positive symptom severity is related to higher thalamic glutamate levels and cognitive deficits to lower dACC glutamate levels during the first two years of illness. Furthermore, higher thalamic glutamate levels after two years are associated with more severe negative symptomatology. Findings imply that glutamatergic compounds decreasing thalamic and increasing dACC glutamate levels may be beneficial in FEP over the first two years of illness.